Device for controlling the tension in a web of material being unwound from a roll

ABSTRACT

In controlling the tension in a web of material unwound from a roll, the web passes over a pendulum roll and a control system is connected to the pendulum roll to measure the tension and to determine any deviations from a predetermined tension value. Based on any such deviations, one or a series of setting members are regulated and these setting members adjust the braking action on a brake disc secured to journals supporting the roll of web material and thereby control the tension in the web. Where multiple setting members are used, various combinations of the setting members can be controlled by a single pressure medium in combination with pre-tensioning springs or differential pressure mediums can be used to achieve the desired braking effect.

United States Patent Heimlicher et al.

Oct. 21, 1975 DEVICE FOR CONTROLLING THE Assignee:

Filed:

Appl. No.: 396,316

Inventors: Paul Heimlicher, Bolligen; Jean Rohrer, Bern; Willy Scharer, Papiermuhle, all of Switzerland Maschinenfabrik Wifag, Bern,

Switzerland Sept. 11, 1973 FOREIGN PATENTS 0R APPLICATIONS 1,253,496 1/196] France 242/7543 Primary Examiner lohn W. Huckert Assistant Examinerlohn M. Jillions Attorney, Agent, or Firm-Toren, McGeady and Stanger [57] ABSTRACT In controlling the tension in a web of material unwound from a roll, the web passes over a pendulum roll and a control system is connected to the pendulum roll to measure the tension and to determine any deviations from a predetermined tension value. Based on any such deviations, one or a series of setting members are regulated and these setting members adjust the braking action on a brake disc secured to journals supporting the roll of web material and thereby control the tension in the web. Where multiple setting members are used, various combinations of the setting members can be controlled by a single pressure medium in combination with pre-tensioning springs or differential pressure mediums can be used to achieve the desired braking effect.

11 Claims, 18 Drawing Figures U.S. Patent Oct. 21, 1975 Sheetlofll 3,913,855

U.S. Patent 0.21, 1975 Sheet20fll 3,913,855

US. Patent Oct.21, 1975 Sheet3of11 3,913,855

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US. Patent Oct. 21, 1975 SheetSofll 3,913,855

U.S. Patent Oct.21,1975 Sheetfiofll 3,913,855

U.S. Patent Oct. 21, 1975 Sheet7ofl1 3,913,855

US. Patent Oct.21, 1975 Sheet80f1l 3,913,855

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US. Patent 0a. 21, 1975 Fig. 11

i E lll 7' 1 aim? US Patent Oct.21,1975 Sheet 10 0H1 3,913,855

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DEVICE FOR CONTROLLING THE TENSION IN A WEB OF MATERIAL BEING UNWOUND FROM A ROLL SUMMARY OF THE INVENTION The present invention is directed to a device for controlling the tension in a web of material being unwound from a roll and, more particularly, it concerns an arrangement for checking the tension and for controlling members which regulate the braking action in a payout-control braking system acting on the roll of material.

It has been known from U.S. Pat. No. 2,974,894, issued Mar. l4, I961, to use signals obtained from a web tension measuring device to control effectively the tension in a web as it runs from one roll to another and, particularly, to effect such control where tension variations occur across the width of the web. The arrangement disclosed in the patent is complex and expensive, and it has no effect on the brake discs firmly connected with the rotatable journal inserted into the roll of material.

In US. Pat. No. 1,883,222, issued Oct. l8, I932, a paper roll braking device is disclosed in which a plurality of brake shoes act directly against the web to be braked. The brake shoes are effective as long as the web of material passes in front of them. It is not possible to connect or disconnect the brake shoes by means of a control circuit. When a roll is being replaced, the brake shoes are temporarily disengaged. In this braking device, the problem exists that, when the brake shoes move into a new zone of the web, bulges develop in the roll of material which are undesirable.

Other devices are known in the art in which a plurality of brakes are sequentially actuated. The disadvantage in such devices is that they require additional control circuits and, as a result, the control system is very complicated and expensive. Furthermore, in such devices it is not possible to use a single pressure medium feed line, rather a separate line is required for each of the brakes. This arrangement is particularly inconvenient if the brakes are mounted on levers fitted on a rotating shaft, because the provision of stuffing boxes causes difficulties.

Therefore, it is the primary object of the present invention to provide an effective device for controlling the tension in a web of material being unwound from a roll while avoiding the shortcomings experienced in the past.

In accordance with the present invention, as the web is unwound it passes over a pendulum roll and a control system is connected to the roll for establishing a control value and determining any deviations from the control value. When deviations occur, the signals in the control system are amplified and transmitted to setting members which adjust the braking action on brake discs firmly attached to rotatable journals inserted into the roll of material from which the web is unwound. As the web is withdrawn from the roll, its tension is checked by the pendulum roll and any deviations from the predetermined control tension value are converted within the control system into a suitable setting value which adjusts the tension through setting members operatively associated with the braking discs.

Due to a number of different parameters affecting the web of material, the control system must be able to afford adjustment over a wide range. The following list of parameters indicates the variations for which the control system must afford adjustment.

1. For processing a web of material, for example in printing, a differential of 5 to 50 kgs. per meter of web width may be required, accordingly, there is an adjustment range of 1:10.

2. In the event of adjustable paper width, the overall tension has to be modified if the web tension set forth in item I above is to be maintained, for instance, in a width ranging from A to 4/4, there is an adjustment range of 1:4.

3. An additional adjustment is required as the web of material is unwound from a roll based on the thickness or radius dimension of the material on the roll. Where a roll has a starting diameter of 1,100 mm. and when unwound has a diameter of 1 10 mm., its adjustment range is 1:10.

4. Where changes in the machine speed occur, the

roll must be accelerated or decelerated. In particular, when deceleration is required as the result of an emergency stoppage, a great braking effect is required in a very brief period and may constitute a multiple of the normal paper tension. The parameters in items l-3 above require an adjustment range of considerable breadth, for instance:

1110 x A x [/10 1/400 If an emergency stoppage takes place, the tension in the material must not drop to zero nor rise into the range of the web breaking strain. In other words, the web tension control system must afford adequate control even when an emergency stoppage takes place. In the case of an average tension on the web material of about 20 kg./m. and a roll diameter of l,l0() mm., an emergency stoppage requires about four times the usual braking effect. Accordingly, if the pressure medium used in operating the control system is compressed air under a pressure of five atmospheres, only one atmosphere is used for the normal tension adjustment whereas four atmospheres required for emergency stoppage are not used in normal operation.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. I is a schematic illustration of the control system embodying the present invention;

FIG. 2 is a sectional view of a portion of the system shown in FIG. 1;

FIG. 3 is a cross-sectional representation of a pair of the setting members shown in FIG. 2;

FIG. 4a is a sectional view of four setting members with only one setting member effecting a braking action;

FIG. 4b is a partial representation of the showing in FIG. 4a with two of the setting members efi'ecting a braking action;

FIG. 4c is similar to FIG. 4b and shows three setting members providing the braking action;

FIG. 4d is similar to FIGS. 4b and 40 with all of the setting members combining to provide the braking ac tion. that is the complete braking power;

FIG. 5 is a graphic representation of the braking action illustrated in FIGS. 4a 4d;

FIG. 6 is a schematic showing of an arrangement utilizing eight setting members;

FIG. 7 is a side view of the arrangement shown in FIG. 6;

FIG. 8 is a partial sectional view of setting members connected to a braking clamp;

FIG. 9 is a sectional view of a setting member including a diaphragm seal;

FIG. 10 is a sectional view of an arrangement similar to FIG. 8 with two series-arranged setting members operatively associated with a braking clamp;

FIG. 11 is a schematic showing of braking clamps each associated with a pair of setting members;

FIG. 12 is a side view of the arrangement shown in FIG. 11;

FIG. 13 is a side view, similar to FIG. 12, illustrating an alternate arrangement of the setting members;

FIG. I4 is a schematic representation of the setting members utilizing counter-pressure; and

FIG. 15 is a schematic representation of an embodiment, similar to FIG. 14, utilizing subtraction relays in combination with the setting members.

DETAILED DESCRIPTION OF THE INVENTION In FIG. I, a web 2 of material is being withdrawn from a roll I of the material and a braking action is applied to the roll for effecting the desired tension in the web. As the web 2 is removed from the roll, it passes over a pendulum roller 3 and a control system is connected to the pendulum roller for determining the actual tension in the web 2.

The control system consists of a control valve transmitter 4 and an operating value monitor 5 which measures any deviations in the tension from the predetermined control value. A regulating device 6 is arranged in communication with the control value transmitter 4 and the operating value monitor 5 for removing signals from both of these devices and, based on the signals received, transmitting a setting value to the setting memher 7 for adjusting, if necessary, the tension in the web. In the following description of the invention, the braking action on the roll is obtained by the action of four brake pistons selectively operatively associated with disc brakes.

In FIG. 2, the apparatus is shown for transmitting the setting value from the regulating device 6 over a line 8 to four setting members 70, 7b, 7c and 7d. Each pair of setting members 7a and 7b, 7c and 7d, is associated with a brake disc 9 and generates the required braking effect which is transmitted by the brake discs to the journals 10 to which the brake discs are fixed. The journals 10 are rotatably supported in brackets 11 mounted on a shaft 12 supported in a machine frame 13. As illustrated in FIG. 2, the journals 10 fit into the roll of material being unwound and rotate with the roll.

In FIG. 3, the arrangement of the setting members associated with the brake disc is shown enlarged, as compared to FIG. 2, and each setting member forms a chamber containing a piston 14 and a pre-tensioning spring 15. A nut 17 positioned within the chamber and in contact with the spring 15, effects the pre-tensioning of the spring. The combination of the pressure medium supplied through line 8 into the chamber of the setting member and the pre-tensioning spring control the displacement of a brake lining 16 positioned on the piston which contacts the surface of the brake disc 9 exteriorly of the chamber within the setting member.

In FIGS. 4a to 4d, variable control of the braking action is indicated by a variable adjustment of the pretensioning springs within the setting members Ia-7d. In FIG. 401, only the brake lining I6 of the piston 14 within the chamber of setting member 7a is displaced into engagement with the brake disc 9, the brake linings 16 associated with the other setting members are maintained in spaced relation from the associated brake disc because of the differential pretensioning provided in the different setting members. In the arrangement shown in FIGS. 4a-4d, the pretensioning is arranged in an increasing manner from setting member 7a to setting member 7d. If, due to the signals received from the monitor 5, an increasing pressure is transmitted through the line 8 to the setting members and is of such a value that it overcomes the pre-tensioning of the spring 15 in the setting member 7b, then the brake linings 16 associated with both of the setting members 70, 7b become effective while the brake linings associated with setting members and 7d remain ineffective, that is, in spaced relation from the associated brake disc 9. In FIG. 4b, the brake linings 16 are shown in engagement with the lefthand brake disc 9 while the brake linings 16 associated with the setting elements 7c and 7d remain spaced from the righthand brake disc 9. If the pressure transmitted through the line 8 from the regulating device 6 is increased further, for instance in the case of an emergency stoppage, the pretensioning springs in setting members 7c and 7d are overcome and their pistons 14 are displaced so that the brake linings 16 move into contact with the associated brake disc 9, note FIG. 40 where all but the brake lining of the setting member 7d contacts the brake discs and FIG. 4d where all of the brake linings contact the brake discs.

In FIG. 5, the effect of this variable braking action is shown graphically with the braking effect B measured along the vertical ordinate and the pressure P of the pressure medium measured along the abcissa or horizontal ordinate. V V and 1., represent the effect of the pre-tensioning springs in setting members 7b, 7c and 7d, respectively. In this graph, the value of the pretensioning action on the spring 15 in the setting mem ber 7a is assumed to be equal to zero. As can be seen, with the exception of the braking effect B the effect of the tensioning spring must be overcome before any braking action occurs. Further, the relative braking effect of the combined braking actions is indicated.

Though in FIGS. 2-4a to 4d a pair of setting members is associated with each brake disc 9, a great variety of arrangements of the setting members can be provided. For instance, in FIGS. 6 and 7, eight setting members are associated with a single brake disc 9 with the setting members being arranged in pairs and being spaced equiangularly apart about the periphery of the brake disc.

The setting members described thus far have had the brake lining 16 located on the piston 14, however, in FIG. 8 the brake lining I6 is mounted on a braking clamp operatively connected to a setting member 7a. By applying the pressure medium through the line 8 into the chambers within the setting member 70, two chambers are provided as compared to the single chamber arrangement shown in FIG. 3, and the clamps are positioned for biasing the brake lining against the brake disc 9.

In FIG. 9, a diaphragm seal is provided within the chamber of the setting member so that it separates the inlet of the pressure medium into the chamber from the piston 14.

As an alternative to the arrangement shown in FIG. 8, FIG. shows a setting member 70 containing a pair of seriesarranged chambers for operating the braking clamp. In FIG. 10 the chamber of the setting member 7a is divided into two sub-chambers each containing a separate piston 14a, 14b and spring a, 15b. Initially, the pressure acting through line 8 acts only on piston 14a and is reduced at first by the countereffect of the spring 15a. As the pressure increases the piston 14b is displaced against the effect of the spring 15b and after it traverses the distance a it contacts the piston 14a and the combined effect of both pistons affords an increased braking effect. Another alternative is shown in FIG. 11 where a pair of laterally spaced setting members are associated with a braking clamp. Each of the setting members is connected to the line 8 and a variable action can be provided by means of the pretensioning springs within the setting members. In FIG. 12, a side view of FIG. 11 shows the setting members located one above the other on the lower end of the braking clamp. In FIG. 13, instead of the superposed arrangement of FIG. 12, the setting members are arranged in side-by-side relationship on the braking clamp.

In FIG. 14, an arrangement of setting members a- 20d is illustrated in which a counter-pressure affords the differential braking action of the setting members. In setting member 200 only one side of the doubleacting piston is supplied with a pressure medium through a branch off the line 8 which is controlled by the regulating device 6. In the other three setting members 20b-20d a pressure medium line is connected on the opposite side of the piston from the side acted on by the pressure medium received from the branch line off the line 8. The counter-pressure is provided through a line 18 which is connected to each of the pressurereducing valves l9b-l9d associated with the setting elements 20b-20d, respectively. The pressure-reducing valves supply a variable counter-pressure to the opposite sides of the pistons in the setting members 20b-20d. As the pressure supplied through the line 8 overcomes the counter-pressure in each of the chambers of the setting members 20b-20d, the corresponding pistons in these setting members are displaced into contact with the brake disc 9 producing the required braking power. This arrangement is similar to that shown in FIG. 4a where the counter-pressure is provided by the pre-tensioning springs and where each spring has a different tensioning effect. Similarly, in FIG. 14 the pressure-reducing valves can be arranged so that the counter-pressure increases from setting member 2012 to setting member 20d.

In FIG. 15, another arrangement is shown, similar to FIG. 14, however, instead of the pressure-reducing valves, subtraction relays Zlb-Zld are used for providing a variable braking effect in each of the setting members. The setting member 20a receives the pressure medium directly from the line 8 controlled by the regulating device 6, however, each of the other setting members has a branch line connected from the line 8 to the subtraction relays 2lb-2ld. A spring 22b, 22c, 22d is associated with each of the subtraction relays 21b, 2 I0, 21d, respectively, and by means of the springs the relays are set to a desired initial pressure. Accordingly, the pressure supplied through the line 8 and controlled by the regulating device 6 must overcome the counteracting force of the springs 2217-2211 before the corresponding setting members become effective. Accordingly, a differential initial pressure controlling each of the setting members is provided so that a variable braking power can be applied to the brake discs.

With the various embodiments of the invention described, it is possible to afford a wide range of adjustment in applying the braking action to the journals on which the roll being unwound is supported. As a result, the adjustments needed for the different parameters of the roll and the web can be accommodated.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. Device for controlling the tension in a web of material being unwound from a roll by means of a pay-out control braking action, .comprising a machine frame, a

shaft mounted in said frame, a bracket mounted on said shaft, a rotatable journal mounted in said bracket and arranged to be inserted into and to rotate with the roll of material to be unwound and a pendulum roll positioned in the path of the web of material as it is unwound from the roll with the web passing over and in contact with a portion of the surface of said pendulum roller, wherein the improvement comprises a control system connected to said pendulum roller, said control system comprises a control value transmitter in communication with said pendulum roller for establishing the tension in the web passing over said roller, an operating value monitor in communication with said pendulum roller for measuring any deviations of the tension in the web from the tension value set in said transmitter, a regulating device in communication with said control value transmitter and said operating value transmitter for receiving signals therefrom, a brake member secured to said journal, a plurality of separate setting members each disposed in communication with said regulating device and each arranged to be operatively associated with said brake member at a difi'erent value transmitted from said regulating device for providing a multiple effect braking action for regulating the tension in the web of material to be unwound from the roll, and countereffect means within said setting members for restraining the operative association at least of certain of said setting members with said brake member and acting in opposition to the value transmitted to said setting members by said regulating device.

2. Device, as set forth in claim I, wherein said brake member is a brake disc, each said setting member comprises means forming a chamber, a braking piston displaceably mounted within said chamber, a line connected to said chamber for admitting a pressure medium into said chamber, said countereffect means comprises means for biasing said braking piston in the direction opposite to the direction of said braking piston as biased by the pressure admitted through said line, said setting member includes means displaceable by said braking piston for effecting the braking action on said brake disc, and said line connected to said regulating device which controls the pressure of the pressure medium into said chamber.

3. Device, as set forth in claim 1, wherein said braking member is a brake disc, each said setting member comprises means forming a chamber, a braking piston displaceably mounted within said chamber, a line con nected to said chamber for admitting a pressure medium into said chamber, said countereffect means comprises means for biasing said braking piston in the direction opposite to the direction said braking piston is biased by the pressure admitted through said line, said setting member includes means displaceable by said braking piston for effecting the braking action on said discs, said line connected to said regulating device which controls the pressure of the pressure medium admitted into said chamber, said means for effecting the braking action comprises a braking clamp operatively connected to said setting member, a brake lining mounted on said braking clamp and arranged to be displaced into contact with said brake disc, said braking piston arranged to operate said brake clamp for displacing said brake linings against said brake disc.

4. Device, as set forth in claim 1, wherein each said setting member comprises means forming a chamber, at least certain of said setting members having a double-acting piston within said chamber, each of said chambers containing a double-acting piston including a first line connected to said chamber for supplying pressure medium to one side of said piston, said first line controlled by said regulating device, a seond line connected to said chamber on the other side of said piston for supplying another pressure medium thereto separate from the pressure medium supplied through said first line, and an adjustable pressure-reducing valve positioned in said second line for varying the pressure medium supplied to the other side of said piston so that differential pressure can be applied to the opposite sides of said braking piston.

5. Device, as set forth in claim 1, wherein said brake member is a brake disc, each said setting member comprises means forming a chamber, a braking piston displace-ably mounted within said chamber, a substraction relay associated with at least certain of said setting members, a first line connected between said regulating device and said subtraction relay for actuating said subtraction relay, a second line connected to said subtraction relay for supplying the pressure medium into said relay, a third line connected between said subtraction relay and said chamber for supplying pressure medium from said relay into said chamber, a spring positioned within said relay for establishing a desired initial pressure within each said setting member with which said relay is associated, said springs within said relay each affording a different initial counter-pressure whereby a differential pressure is available in different said setting members for varying a braking action on said journal.

6. Device, as set forth in claim 2, wherein said means for pre-tensioning said braking piston comprises a pretensioning spring within said chamber in contact with said braking piston, and an adjustable member positioned within said chamber in contact with said spring and movably positionable within said chamber for pretensioning said spring and establishing a biasing action on said piston acting oppositely to the pressure medium admitted into said chamber.

7. Device, as set forth in claim 2, wherein said means for effecting the braking action comprises a brake lining mounted on said braking piston and arranged to be displaced into contact with said brake disc.

8. Device, as set forth in claim 2, wherein a diaphragm seal is mounted in said chamber of said setting member and separates the inlet of the pressure medium from said braking piston.

9. Device, as set forth in claim 2, wherein said setting members are arranged in series.

10. Device, as set forth in claim 2, wherein said setting members are arranged in parallel.

11. Device, as set forth in claim 2, wherein at least two of said setting members are combined to form a cumulative effect of said braking pistons acting on said brake disc. 

1. DeVice for controlling the tension in a web of material being unwound from a roll by means of a pay-out control braking action, comprising a machine frame, a shaft mounted in said frame, a bracket mounted on said shaft, a rotatable journal mounted in said bracket and arranged to be inserted into and to rotate with the roll of material to be unwound and a pendulum roll positioned in the path of the web of material as it is unwound from the roll with the web passing over and in contact with a portion of the surface of said pendulum roller, wherein the improvement comprises a control system connected to said pendulum roller, said control system comprises a control value transmitter in communication with said pendulum roller for establishing the tension in the web passing over said roller, an operating value monitor in communication with said pendulum roller for measuring any deviations of the tension in the web from the tension value set in said transmitter, a regulating device in communication with said control value transmitter and said operating value transmitter for receiving signals therefrom, a brake member secured to said journal, a plurality of separate setting members each disposed in communication with said regulating device and each arranged to be operatively associated with said brake member at a different value transmitted from said regulating device for providing a multiple effect braking action for regulating the tension in the web of material to be unwound from the roll, and countereffect means within said setting members for restraining the operative association at least of certain of said setting members with said brake member and acting in opposition to the value transmitted to said setting members by said regulating device.
 2. Device, as set forth in claim 1, wherein said brake member is a brake disc, each said setting member comprises means forming a chamber, a braking piston displaceably mounted within said chamber, a line connected to said chamber for admitting a pressure medium into said chamber, said countereffect means comprises means for biasing said braking piston in the direction opposite to the direction of said braking piston as biased by the pressure admitted through said line, said setting member includes means displaceable by said braking piston for effecting the braking action on said brake disc, and said line connected to said regulating device which controls the pressure of the pressure medium into said chamber.
 3. Device, as set forth in claim 1, wherein said braking member is a brake disc, each said setting member comprises means forming a chamber, a braking piston displaceably mounted within said chamber, a line connected to said chamber for admitting a pressure medium into said chamber, said countereffect means comprises means for biasing said braking piston in the direction opposite to the direction said braking piston is biased by the pressure admitted through said line, said setting member includes means displaceable by said braking piston for effecting the braking action on said discs, said line connected to said regulating device which controls the pressure of the pressure medium admitted into said chamber, said means for effecting the braking action comprises a braking clamp operatively connected to said setting member, a brake lining mounted on said braking clamp and arranged to be displaced into contact with said brake disc, said braking piston arranged to operate said brake clamp for displacing said brake linings against said brake disc.
 4. Device, as set forth in claim 1, wherein each said setting member comprises means forming a chamber, at least certain of said setting members having a double-acting piston within said chamber, each of said chambers containing a double-acting piston including a first line connected to said chamber for supplying pressure medium to one side of said piston, said first line controlled by said regulating device, a seond line connected to said chamber on the other side of said piston for suppLying another pressure medium thereto separate from the pressure medium supplied through said first line, and an adjustable pressure-reducing valve positioned in said second line for varying the pressure medium supplied to the other side of said piston so that differential pressure can be applied to the opposite sides of said braking piston.
 5. Device, as set forth in claim 1, wherein said brake member is a brake disc, each said setting member comprises means forming a chamber, a braking piston displaceably mounted within said chamber, a substraction relay associated with at least certain of said setting members, a first line connected between said regulating device and said subtraction relay for actuating said subtraction relay, a second line connected to said subtraction relay for supplying the pressure medium into said relay, a third line connected between said subtraction relay and said chamber for supplying pressure medium from said relay into said chamber, a spring positioned within said relay for establishing a desired initial pressure within each said setting member with which said relay is associated, said springs within said relay each affording a different initial counter-pressure whereby a differential pressure is available in different said setting members for varying a braking action on said journal.
 6. Device, as set forth in claim 2, wherein said means for pre-tensioning said braking piston comprises a pretensioning spring within said chamber in contact with said braking piston, and an adjustable member positioned within said chamber in contact with said spring and movably positionable within said chamber for pretensioning said spring and establishing a biasing action on said piston acting oppositely to the pressure medium admitted into said chamber.
 7. Device, as set forth in claim 2, wherein said means for effecting the braking action comprises a brake lining mounted on said braking piston and arranged to be displaced into contact with said brake disc.
 8. Device, as set forth in claim 2, wherein a diaphragm seal is mounted in said chamber of said setting member and separates the inlet of the pressure medium from said braking piston.
 9. Device, as set forth in claim 2, wherein said setting members are arranged in series.
 10. Device, as set forth in claim 2, wherein said setting members are arranged in parallel.
 11. Device, as set forth in claim 2, wherein at least two of said setting members are combined to form a cumulative effect of said braking pistons acting on said brake disc. 